A diesel fuel is a complex liquid mixture including-among many other things-aromatics and alkanes (paraffins). When the temperature is lowered below a threshold value (TPS), a paraffin-rich solid phase separates from an aromatic-rich liquid phase. Up-to-date diesel fuels include additives whose role is to lower the value of TPS. We studied one of these additives, in a model mixture made of ethylbenzene and hexadecane, as a function of temperature in the liquid phase. The additive is a comb-like oligomer, with alkyl side chains. From static and dynamic light scattering experiments and optical interference microscopy observations, we found that below a transition temperature T*(T*> TPS) the mixture self-organizes into a colloidal phase made of micrometer-sized aggregates. These aggregates are found to be anisotropic in shape and highly lacunary in terms of their content in additive molecules. These supramolecular structures play the key role in the additive efficiency. © 1992.
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